The present invention pertains to a device for clamping and welding plates which are in contact with one another, preferably for use in automobile manufacturing.
It has been known in the manufacture of bodies that both a clamping tool and a laser welding head can be fastened to a robot arm. Various clamping tools are available for welding plates that are in contact with one another. Either the clamping tools are moved together with the laser welding head for welding on the components or the clamping tool is pressed firmly against the components and subsequently released for preparing a weld seam. Preparing a weld seam of a length of, e.g., several cm is problematic in the case of a moving clamping tool because, among other things, displacement may occur between the components.
A device for welding, especially laser welding, with a welding head has been known from EP 0 734 304 B1. The plates are now lying on a support during the processing and are pressed on by means of a spring-tensioned pressing device. The pressing device and the welding head are fastened to the hand of a manipulator and are thus moved corresponding to the course of the weld seam. Sensors, e.g., distance, force or pressure sensors, are additionally arranged at the holding-down device in order to determine whether the holding-down device and the workpiece are in contact with one another or to detect a locally occurring pressure. The welding beam is directed in this prior art toward the upper plate and the contact with the subjacent plates is established by the upper plate. No provisions are made for welding with a welding beam which is directed into the welding gap between the plates that are in contact with one another. This is expediently done with prior-art clamping tools.
Special attention must be paid to the accurate positioning of the plate edges in relation to one another because the plate edges may have unevennesses and damage may occur especially in the case of thin plates.
The basic object of the present invention is therefore to provide a device for clamping and welding in which accurate and lasting clamping and positioning of the plates that are in contact with one another is maintained in relation to one another and to the welding head directed into the welding gap between the plates for preparing an accurate weld seam.
According to the invention, a device for clamping and welding plates is provided for plates that are in contact with one another, preferably for use in automobile manufacture. A bracket is fastened to a mounting flange, preferably of a robot arm. The bracket carries a clamping tool and a welding head. An energy beam of the welding head is directed into the welding gap between the plates. The bracket and/or the welding head is movable in a linear guide by means of the mounting flange in relation to the clamping tool corresponding to the course of the weld seam. Stop elements are arranged on the clamping tool for positioning the plates in relation to one another and/or to the welding head for detecting the position of the edges of at least one of the plates.
A locking device may be provided which prevents a relative movement between the bracket and the clamping tool for positioning the clamping tool at the plates. The locking device may be arranged at the bracket. The locking device may include a pneumatic cylinder.
The clamping tool may be designed as a gripping jaw with a hydraulic cylinder. The stop elements may be arranged on an arm of the gripping jaw, which arm is located opposite the hydraulic cylinder. The edges of the plates located in contact with one another, which edges are to be welded together, may be located in different planes and the stop elements may detect only the position of the edge of the shorter plate. The stop elements may have stop faces arranged at right angles to one another. Two stop elements may be employed, between which the weld seam is formed. These two stop elements may be arranged at spaced locations from one another in the welding direction.
An opening for the energy beam may be provided with a diameter or length that is greater than the maximum length of the weld seam to be prepared. This opening may be arranged in the arm of the clamping tool. The energy beam may be directed onto the contact surface of the edges of the two plates lying one on top of another at an acute angle to the contact surface.
In the device according to the present invention, the clamping tool, preferably a hydraulically actuated gripping jaw, is mounted by means of a bracket on a freely programmable robot. The laser welding head is also fastened to the bracket at the same time. The bracket and/or laser welding heads can be moved by means of the robot arm in a linear guide in relation to the clamping tool corresponding to the course of the weld seam. Due to this additional linear guide according to the present invention and the mobility in relation to one another, it is possible to first bring the entire device, i.e., the bracket and the laser welding head with the clamping tool, to the welding site and to firmly brace the plates to be welded by means of the clamping tool after accurate positioning. Stop elements preferably designed as feelers for detecting the plate edges may be arranged on the clamping tool for positioning the plates. After positioning and clamping the plates, it is possible due to the linear guide to move the bracket and the laser welding head relative to the plates and the gripping jaw and to prepare a weld seam of a length of, e.g., a few cm as a result. The special advantage of this device is that the clamping tool and the plates are not moved during the movement of the laser welding head and remain firmly in their accurate position.
It has proved to be favorable to additionally arrange a locking device on the bracket in order to prevent a relative movement between the bracket and the clamping tool during the positioning of the clamping tool. This locking device may advantageously comprise a pneumatic cylinder, which acts, e.g., in the direction of the linear guide and fixes the clamping tool at one end of the linear guide.
The clamping tool may be designed according to the present invention as a gripping jaw with a hydraulic cylinder, which preferably acts at right angles to the longitudinal direction of the linear guide and braces the plates against an arm of the gripping jaw. The ends of two plates lying one on top of another are thus positioned with their cut edges directly at the stop elements and are then braced by the hydraulic cylinder with the arm of the gripping jaw. However, it is sufficient to grasp only the edge of the shorter plate by means of the stop elements in the case of different heights of the plate edges. The stop elements may be arranged at spaced locations from one another in the welding direction.
The distance is preferably selected to be such that a sufficiently long weld seam of, e.g., several cm, can be prepared between the stop elements.
The laser beam of the laser welding head is directed toward the contact surface at a certain angle, especially an acute angle to the contact surface of the two plates lying one on top of another. To set the incidence angle of the laser beam, a suitable guide is provided for this purpose on the bracket. After clamping the plates in the gripping jaw, the locking cylinder is first switched so as to release the pressure and the linear guide is thus unlocked in order for it to be subsequently able to be moved linearly along the plate edges to be welded together by means of the robot arm of the laser welding head. The servo drive of the robot arm, which is usually present, is used for the movement, so that the laser weld seam is prepared, the preparation of the seam being able to be regulated with a freely selectable velocity profile. As a result, an accurate and uniform welding can be performed in a very short time.
It has proved to be favorable to provide a window-like opening for the laser beam, whose diameter or length is greater than the maximum length of the weld seam to be prepared, in one arm of the gripping jaw. After the conclusion of the welding operation, the hydraulic cylinder of the gripping jaw is released and the robot arm can be displaced to the next welding site. The locking cylinder is again closed during this displacement operation in order to establish an accurate position of the clamping tool in relation to the bracket.